3.11 Stem Cells

Question 1

What are stem cells?

Answer 1

unspecialised cells that can differentiate into specialised cells

Question 2

How do stem cells divide?

Answer 2

by mitosis

Question 3

What is totipotency? Where are totipotent cells found?

Answer 3

• the ability to produce all cell types, including extraembryonic cells (cells of the placenta and umbilical chord)
• found in the first 8 cells (after 3 divisions)

Question 4

What is pluripotency? Where are pluripotent cells found?

Answer 4

• the ability to produce all specialised cells except extraembryonic cells (the genes for these cells have become inactivated)
• found in the embryo (inner cell mass)

Question 5

What is multipotency? Where are multipotent cells found?

Answer 5

• the ability to produce some specialised cells
• found in adult tissues (e.g. bone marrow)

Question 6

Describe the formation of different stem cell types:

Answer 6

1. a zygote forms after fertilisation
2. after 3 cell cycles, there are 8 cells
3. these are totipotent
4. after further cell division, a blastocyst forms
5. the extraembryonic cells form the placenta and umbilical chord (can only be produced from totipotent cells)
6. the inner cell mass forms the embryo
7. these embryonic stem cells are pluripotent
8. these stem cells become increasingly specialised as an embryo develops
9. some adult cells are stem cells - these are multipotent

Question 7

Describe the function of plant stem cells:

Answer 7

• plant stem cells = meristem
• are totipotent
• used for growth and repair of new tissue in roots and shoots